Polyamide-imides and precursors thereof

ABSTRACT

POLYAMIDE-IMIDES HAVING HIGH THERMAL AND MECHANICAL STABILITY FORMED AT LOW COST BY PYROLYTICALLY POLYMERIZING NOVEL PREPOLYMERS OF IMPROVED SOLUBILITY CHARACTERIZED BY THE GENERAL FORMULA   E1-(R1-N&lt;(-CO-)2&gt;R3-CO-NH-R2-NH-CO-R3&lt;(-CO-)2&gt;N)N-R1-E2   WHERE: E1 AND E2 ARE INDIVIDUALLY SELECTED FROM THE CLASS CONSISTING OF   1,3-DI(O=),7A-Y1,3A-Y2,4-Y3,5-Y4,6-Y5,7-Y6,8-(Y7-X-)-1,3-   3A,4,7,7A-HEXAHYDRO-4,7-METHANOISOINDOL-2-YL WHERE C8 IS   Y8, AND 2,5-DI(O=),3-Y2,4-Y1-3-PYRROLIN-1-YL   WHERE: X IS A MEMBER OF THE CLASS CONSISTING OF CARBON, OXYGEN, SULFUR, AND CARBONYL Y1-Y6; AND Y7 AND Y8 WHEN PRESENT, ARE INDIVIDUALLY SELECTED FROM THE CLASS CONSISTING OF HYDROGEN, AROMATIC GROUPS, SUBSTITUTED AROMATIC GROUPS, SATURATED OR UNSATURATED HYDROCARBON GROUPS HAVING FROM 1 TO 6 CARBON ATOMS, ALKYL ETHERS, ARYL ETHERS, HALOGENS, AND NITRO GROUPS; R1 AND R2 ARE INDIVIDUALLY SELECTED FROM THE CLASS CONSISTING OF AROMATIC GROUPS, SUBSTITUTED AROMATIC GROUPS, SATURATED AND UNSATURATED HYDROCARBON GROUPS, SATURATED AND UNSATURATED HETEROCYCLIC GROUPS, AND MIXTURES THEREOF; R3 IS SELECTED FROM THE CLASS CONSISTING OF SUBSTITUTED AROMATIC GROUPS, UNSUBSTITUTED AROMATIC GROUPS, SATURATED CYCLIC GROUPS, UNSATURATED CYCLIC GROUPS, SATURATED HETEROCYCLIC GROUPS, AND UNSATURATED HETEROCYCLIC GROUPS; AND N IS ONE OR MORE FOR A SINGLE PREPOLYMER AND STATISTICALLY GREATER THAN 0 FOR A MIXTURE;   THE POLYAMIDE-IMIDES MAY ALSO BE FORMED BY PYROLYTICALLY POLYMERIZING THE NOVEL AMIC-ACID PRECURSORS OF SAID PREPOLYMERS WHICH ARE CHARACTERIZED BY THE FORMULA   E3-(R1-NH-CO-R3(-COOH)-CO-NH-R2-NH-CO-R3(-COOH)-CO-NH)N-   R1-E4   WHERE:   E3 AND E4 ARE INDIVIDUALLY SELECTED FROM THE CLASS CONSISTING OF   1-Y6,2-Y1,2-((-)NH-CO-),3-(HOOC-),3-Y2,4-Y3,5-Y4,6-Y5,   1,4-(-Y8(-X-Y7)-)CYCLOHEX-5-ENE, AND -NH-CO-C(-Y)=C(-Y2)-   COOH   WHERE: X1, Y1-Y6 AND Y7 AND Y8 ARE DEFINED AS DEFINED ABOVE; AND R1, R2, R3 AND N ARE AS DEFINED ABOVE.   THE PYROLYTICALLY POLYMERIZED PREPOLYMER IS USEFUL AS AN ADHESIVE, MOLDING COMPOSITION, COATING, OR AS A MATRIX MATERIAL IN THE PREPARATION OF HIGH STRENGTH LAMINATES AND COMPOSITES.

United States Patent Hyman ABSTRACT OF THE DISCLOSURE Polyamide-imides having high thermal and mechanical stability formed at low cost by pyrolytically polymerizing novel prepolymers of improved solubility characterized by the general formula l ii where: E and B are individually selected from the class consisting of and where: X is a member of the class consisting of carbon, oxygen, sulfur, and carbonyl Y -Y and Y and Y when present, are individually selected from the class consisting of hydrogen, aromatic groups, substituted aromatic groups, saturated or unsaturated hydrocarbon groups having from 1 to 6 carbon atoms, alkyl ethers, aryl ethers, halogens, and nitro groups;

R and R are individually selected from the class consisting of aromatic groups, substituted aromatic groups, saturated and unsaturated hydrocarbon groups, saturated and unsaturated heterocyclic groups, and mixtures thereof;

R is selected from the class consisting of substituted aromatic groups, unsubstituted aromatic groups, saturated cyclic groups, unsaturated cyclic groups, saturated heterocyclic groups, and unsaturated heterocyclic groups; and

1 is one or more for a single prepolymer and statistically greater than 0 for a mixture;

The polyamide-imides may also be formed by pyrolytically polymerizing the novel amic-acid precursors of said prepolymers which are characterized by the formula L -t A t .1,

ice

where:

E, and B are individually selected from the class consisting of where: X Y -Y and Y and Y are defined as defined above; and R R R and 1 are as defined above.

The pyrolytically polymerized prepolymer is useful as an adhesive, molding composition, coating, or as a matrix material in the preparation of high strength laminates and composites.

BACKGROUND OF THE INVENTION (A) Field of the invention This invention relates in general to the field of synthetic polymeric resins. More particularly, it relates to improvements in polyamide-imide polymerizates, useful products made therefrom, their prepolymers, precursors, and their manner of preparation. Still further, this invention relates to rapid curing, stable, high molecular weight polyamide-imides formed by pyrolytically polymerizing polyamide-imide prepolymers and polyamic-acid precursors.

(-B) Description of the prior art The need for synthetic materials capable of maintaining their properties at elevated temperatures and under exposure to a wide variety of chemical environments has accelerated in recent years. In general the search for such materials has focused on synthetic polymer resin systems. Initially two resin systemsphenolic and silicone, were widely employed. Although those systems possess several important qualities, they have not yielded the combination of physical, chemical, and thermal properties required for many contemporary uses.

As a result, an increasing amount of attention has been directed to polyimides and polyamide-imides. These polymers are generally recognized for their outstanding physical and chemical properties. Presently, polyimides are being marketed as varnishes, coatings for glass fabrics, insulating enamels, self-supporting films, laminating resins, and molded products such as bearings, piston rings, etc.,- where the resin must function at temperatures and under conditions where most other known materials have failed.

However, while presently available polyimides are known to have outstanding physical and chemical properties, which makes them attractive for many applications, the problems encountered in processing and in preparing these polyimides have limited their full potential use. Generally, for example, these polyimides are obtained by synthesizing high-molecular weight or longchain precursor polymers. The precursors are converted to the desired heterocyclic ring polymers by completely imidizing or condensing them, thereby yielding high molecular weight polyimides. However, because these polyimides are almost impervious to solvents, they are now being marketed as-a varnish for making prepregs for glass laminates, etc., in the precursor form. The precursor of polyamide-acids, obtained by linear chain extension or polymerization, is substantially unstable at ambient temperatures and therefore must be kept in solution hermetically sealed and refrigerated to avoid hydrolytic and oxidative degradation. Ultimately, the polymaide-acid'precursors substantially free of solvent are cured by the application of heat for periods ranging up to about 16 hours at substantially elevated temperatures to produce the completely imidized product. This reaction is accompanied by the evolution of an appreciable amount of volatile matter, e.g., residual solvent, water, etc., thus tending to produce voids, for example, in laminated structures.

A significant advance in the field of high performance polyimides is represented by US. Pat. 3,528,950 to Hyman R. Lubowitz. In accordance with the teachings of that patent, rapid-curing, stable polyimides are prepared by heating polyimide prepolymers formed by coreacting end-capping, specific monoanhydrides with mixture of dianhydrides and diamines. The end-capping anhydrides are compounds having the structural formula:

where R represents hydrogen or a lower alkyl.

Whereas the prepolymers and pyrolytically polymerized final polymers described in that patent possess outstanding properties not found in other polyimide polymer sys tems, certain drawbacks of these polymers have been identified. For example, in general, those prepolymers are not readily soluble in organic solvents. As a result it is necessary to employ solutions of the precursors of the prepolymers in the preparation of the final products. Unfortunately, these precursors are unstable with respect to heat and moisture and thus require special precautions in storage and use.

On the other hand, soluble prepolymers are desirable because they can be sold as such and can be transported and stored under atmospheric conditions. They also can be prepared in solution, on-site as the need arises. Since in many cases on-site preparation is a requirement, prepolymers which can be easily transported possess substantial economic advantages.

The utility of the polymers disclosed in US. Pat. 3,528,950 is also somewhat limited by their expense due primarily to the high cost of the aromatic dianhydrides employed. Because of their expense those polymers are limited to only those high-priced applications where very high performance is required such as in the aircraft and aerospace industries.

Another limitation on the use of those polymers is presented by difliculties encountered during resin processing. In most instances these difiiculties are traceable to poor flow characteristics. In certain applications, good flow characteristics are very important. For example, in fabrication of laminates using autoclave or vacuum bag techniques, the required wetting of the fibers is greatly facilitated if the resin has good flow. Previously, it has been necessary to augment flow by maintaining an amount of residual solvent in the resin during fabrication. The benefits of this practice, however, are often offset by the tendency of the solvent to volatilize and cause voids in the cured resin structure.

As a result of the deficiencies of prior art resin systems, there remains in the art a need for an improved polymer resin system which is less expensive and exhibits improved flow characteristics while retaining high performance characteristics at elevated temperatures and during exposure to a wide variety of chemical environments.

4 SUMMARY OF THE INVENTION Briefly, the preferred embodiments of the present in vention present improved polyamide-imides prepared by pyrolytically polymerizing novel polyamide-imide polymers represented by the formula:

\C Ill I l \C/ J l l where E and E are individually selected from the class consisting of where: X is a member of the class consisting of carbon, oxygen, sulfur, and carbonyl; Y Y and Y and Y when present, are individually selected from the class consisting of hydrogen, aromatic groups, substituted aromatic groups, saturated or unsaturated hydrocarbon groups having from 1 to 6 carbon atoms, alkyl ethers, aryl ethers, halogens, and nitro groups.

R and R are individually selected from the class consisting of aromatic groups, substituted aromatic groups, saturated and unsaturated hydrocarbon groups, saturated and unsaturated heterocyclic groups, and mixtures thereof.

R is selected from the class consisting of substituted aromatic groups, unsubstituted aromatic groups, saturated cyclic groups, unsaturated cyclic groups, saturated heterocyclic groups and unsaturated heterocyclic groups; and

n is one or more for a single prepolymer and statistically greater than 0 for a mixture of prepolymers.

The polyamid-imides may also be formed by pyrolytically polymerizing the novel amic-acid precursors of said prepolymers which are characterized by the formula E and E, are individually selected from the class consisting of and Y1 ELE- YJ E--orr where: X Y -Y and Y and Y are as defined above; and R R R and N are as defined above.

The pyrolytically polymerized prepolymer is useful as an adhesive, molding composition, coating, or as a matrix material in the preparation of high strength laminates and composites.

These prepolymers and the precursors thereof are generally soluble in polar solvents. Polymers formed therefrom exhibit improved processability particularly with regard to flow characteristics. They are also less expensive than prior art polymers and in addition exhibit unexpectedly good adhesive properties.

Accordingly, the objects of this invention are:

These and others objects and advantages of the invention will become more apparent to those of ordinary skill in the art upon consideration fo the following description of the preferred embodiments of the invention which includes a description of the best mode of carrying out the invention as presently perceived.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of this invention pertain to the preparation of novel polyimide prepolymers precursors of said prepolymers, final polymers and articles made therefrom as well as to the methods of preparing said polymers and articles.

PREPOLYMERS Prepolymers prepared herein relate to a class of polymers represented by the general formula:

B represents a backbone composition; and

E and E represent end groupings individually selected from the class consisting of and i Y l Y:- C l where:

X is a member of the class consisting of carbon, oxygen, sulfur, and carbonyl; and

Y -Y and Y and Y when present, are individually selected from the class consisting of hydrogen, aro- 'matic groups, substituted aromatic groups, saturated or unsaturated hydrocarbon groups having from 1 to 6 carbon atoms, alkyl ethers, aryl ethers, halogens, and nitro groups.

In U.S. Pat. 3,528,950, the backbone composition was selected from the group of compounds represented by the formula:

where R represents an aliphatic or aromatic group.

As noted above, final polymers made in accordance with that patent represented a substantial advance in the art.

In the present invention, the backbone units correspond to the general formula 1 where:

R and R are individually selected from the class consisting of aromatic groups, substituted aromatic groups, saturated and unsaturated hydrocarbon groups, saturated and unsaturated heterocyclic groups and mixtures thereof.

R is selected from the class consisting of substituted aromatic groups, unsubstituted aromatic groups, saturated cyclic groups, unsaturated cyclic groups, saturated heterolcyclic groups and unsaturated heterocyclic groups; an

1 is one or more for a single polymer or statistically greater than 0 for a mixture of prepolymers.

As a result, the prepolymers can be represented by the formula l H tl '7 It is also contemplated that useful prepolymers can be formed by mixing these compounds with compounds of the general formula where E E and R are defined as above.

The result is that 1 in the general formula for a mixture of prepolymers may statistically range upwards from an amount greater than 0, although 1 is preferably less than about for single prepolymers or in mixtures.

The more preferred prepolymers are those which have 80 to 100 percent of their end groups represented by the formula Furthermore, it is preferred that X in this end grouping is carbon and that Y Y is a member of the class consisting of hydrogen, lower alkyl groups, halogen, and mixtures thereof. Examples of lower alkyl groups which are suitable include methyl, ethyl, propyl, butyl, and amyl. It is preferred that R and R be radicals selected from the class of radicals consisting of aryl, alkyl, cycloalkyl, aralkyl, alkaryl, alkylene, arylene, substituted aryl, substituted alkyl, heterocyclic aryl, substituted aralkyl and mixtures thereof. Although hydrocarbon groups are the preferred species for R R many other groups may also be used. Among the other useful groups are: ethers, mercaptaus, aminos, sulfides, sulfoxides, and sulfones.

By far the preferred species for R is a phenylene group. The reason being that of the reactants which result in the formation of R groups, the most readily available and most economic is trimellitic anhydride. Trimellitic anhydride is a by-product from conventional petroleum cracking processes and is very well suited as a reactant in the formation of the compounds of this invention. However, other groups fitting the above definition of R are also contemplated.

When trirnellitic anhydride is used as a reactant the backbone of the prepolymer will correspond to the formula:

The backbone of the correspondin precursor is represented by:

The arrows indicate both isomer forms are possible.

The preferred manner of preparing the prepolymers and precursors of this invention involves the general steps of reacting an amide with an aromatic group containing carboxylic acid and an anhydride group to form a dianhydride by transamidification; then reacting the dianhydride with a polyfunctional amine and an end-capping anhydride to form the prepolymer or precursor. The most preferred anhydride is trimellitic anhydride.

The starting amide may be formed by reaction of an anhydride with a polyfunctional primary amine. A wide variety of anhydrides may be used for this purpose because the acid portion is removed upon a transamidification. In general, the preferred anhydrides are those characterized by the general formula:

where R is a lower alkyl radical having from 1 to 5 carbon atoms.

It is normally desirable to use an anhydride which, on its reaction with the amine and upon transamidification,

forms an acid by-product that is easily removed from para-phenylene diamine meta-phenylene diamine 4,4'-diamino-diphenyl propane 4,4-diamino-diphenyl methane benzidine 4,4'-diamino-diphenyl sulfide 4,4'-diamino-diphenyl sulfone 3,3-diamino-diphenyl sulfone 4,4-diamino-diphenyl ether 1,5-diamino-naphthalene 3,3-dimethoxy benzidine 2,4-bis(beta-amino-t-butyl) toluene bis-(para-beta-amino-t-butyl-phenyl) ether bis-(para-beta-methyl-delta-amino-pentyl) benzene bis-para-(l,l-dimethyl-S-amino-pentyl) benzene l-isopropyl-2,4-metaphenylene diamine m-xylylene diamine hexamethylene diamine heptamethylene diamine octamethylene diamine nonamethylene diamine decamethylene diamine diamino-propyl tetramethylene diamine B-methylheptamethylene diamine 4,4-dimethylheptamethylene diamine 2,1 l-diaminmdodecane l,2-bis-(3amino-propoxy) ethane 2,2-dimethyl propylene diamine 3-methoxy-hexamethylene diamine 3,3'-dimethyl benzidine 2,5-dimethylhexamethylene diamine 2,5-dimethylheptamethylene diamine S-methyl-nonamethylene diamine 2,17-diamino-cicosadecane 1,4-diamino-cyclohexane 1,10-diamino-1,10-dimethyl decane l,l2-diamino-octadecane.

Triamines such as 1,3,5-triaminobenzene 2,4,6-triamino-s-triazine 1,2,3-triaminopropane 4,4',4"-triaminotriphenyl methane 4,4',4"-triaminotriphenylcarbinol Once the amide is formed, it is reacted with an aromatic group containing carboxylic acid and an anhydride group, preferably as noted above, trimellitic anhydride to form a dianhydride by transamidification. The dianhydride is then reacted with a polyfunctional primary amine and an end-capping anhydride. These reactions may occur together or separately. A wide variety of polyfunctional primary amines may be used including all those previously listed in connection with the formation of the starting amide.

The end-capping anhydrides which may be used are selected from those represented by:

Where: X, and Y -Y are as hereinabove defined.

The first listed formula represents the preferred end group. Mixtures of the two end groups are also preferred and if desired the end group represented by the second listed formula may be used by itself, but not with the equivalent superior results obtained by the use of end groups corresponding to the first listed formula.

The amount of end-group anhydride used in this reaction is preferably controlled so that n is an integer of from 1 to about 10. This amount of anhydride will produce prepolymers having a' molecular weight of from about 500 to 6000.

As a first alternative, the end-capping anhydride may be reacted after reaction of the anhydride product and the polyfunctional amine.

The first listed formula may also be formed in situ as a reaction product where it will then react with the backbone polymer to form the ultimate prepolymer structure. One way of forming the anhydride in situ is to react an appropriate anhydride and a conjugated cyclodiene. For example, maleic anhydride and cyclopentadiene can be reacted to form the endomethylene end groups.

Mixtures of the two end groups can also be formed in this manner by adding less than the equivalent amount of cyclopentadiene.

The several reactions involved in the preparation of prepolymers are preferably carried out in one or more solvent mediums. In general, strong polar organic sol vents are preferred.

Examples of these solvents are tetramethylurea; dimethylsulfoxide; l-methyl-Z-pyrrolidone; pyridine; dimethylsulfone; hexamethylphosphoramide; N,N-dimethylformamide; N,N-dimethyl acetamide; tetramethylenesulfone; dimethyltetramethylenesulfone; and in general, any polar organic solvent which does not react with the polyfunctional amines or polyfunctional anhydrides at the process conditions. Nonpolar solvents such as toluene may be employed in small amounts in conjunction with the above polar solvents as an aid in entraining the prepolymer reaction byproducts, principally water from the reaction site, thereby forming the prepolymer in solution. The resulting solutions as such may be employed as varnishes, for example, in the preparation of prepregs for laminates. If desired, the prepolymers can be prepared in the absence of a solvent media by reaction in a melt form.

A significant advantage of the present invention lies in the fact that the prepolymers are stable and soluble in highly polar organic solvents. This allows the prepolymers to be shipped and stored as such or in solution under atmospheric conditions for later use.

PREPARATION OF PREPOLYMER PRECURSORS Amic acid precursors corresponding to the prepolymers described above can be prepared by carrying out the prepolymer formation reactions at temperatures below about C. These amic acid precursors are compounds represented by the formula .lti s.ttmtfshtm l-H0E 1!! 1 fi-on-L where E and B are individually selected from; the class consisting of I "r Y ll N lYf-X-Yl Y -C-0H Y: a and O H Y:

{L L JIM. Y: g

where: X Y -Y are as defined; and R R R and a are as hereinabove defined.

Mixtures of precursors and the previously described prepolymers are formed if the reaction temperatures are between about 125 C. and 200 C. with the percentage of prepolymer increasing at increasing temperatures within this range. At temperatures above 200 C. the precursors will be condensed and imidizad to the corresponding prepolymer.

The precursors and prepolymers separately or mixed are valuable products in and of themselves. Similarly, solutions of these compounds are valuable. They can be shipped and stored without extraordinary precaution.

PREPARATION OF FINAL POLYMERS Cross-linked polymers, resistant to elevated temperatures and oxidation resistant may be formed without catalysts or coreactive compositions of matter by thermally polymerizing the prepolymers prepared according to this invention.

Polymerization takes place by heating the prepolymer or the precursors of prepolymers to a temperature of from about 225 C. to about 375 C. for a period of time of about 5 minutes to about 2 hours, depending upon the prepolymer or precursor used. If the prepolymer is in solution it is preferable to drive the solvent prior to final curing of the prepolymer. Although the reactions by which the final resins are obtained are not known, it is theorized that the end groups of the polyamide-imide prepolymer molecular chain become reactive at temperatures above C. The result is a coreaction between the end groups linking the prepolymers together to form macromolecules having a molecular weight of about 10,000 or above. These polymers are rapid-curing and stable in high thermal and oxidative environments. For example, polymers prepared in this manner exhibit long term thermal stability at temperatures greater than 500 F.

Due to their superior properties these polymers find utility in a wide variety of applications demanding high performance materials. Uses include adhesives, laminates, composites, coatings, plastic structures and moldings.

PREPARATION AND USE OF ADHESIVES The polymers of the present invention may be used to form excellent high temperature adhesive compositions.

1 1 i a They can be used with a wide variety of adherents using conventional processing techniques.

The prepolymers, for example, may be applied to different surfaces or adherends by coating them with said prepolymers, precursors of said prepolymers or mixtures thereof, in the form of a melt, slurry, or varnish and subsequently applying heat and pressure; thereby causing the prepolymers to polymerize to a higher molecular Weight infusible polymeric bond. More specifically, simultaneously with the thermal polymerization and volatilization of the solvent, the adherends are pressed together at pressures ranging up to about 1,000 p.s.i., e.g., ranging preferably from about200 to 800 p.s.i. at temperatures ranging from about 175 C. to 350 C. or higher to form the plastic bond. The joints obtained under these conditions may either be in the neat form or they may be reinforced with various materials including glass fibers, silicon, graphite, or some other known filler by initially adding the material to the prepolymer prior to forming the adhesive bond. Since the polyimides of this invention adhere to a variety of materials including, for example, metals, nonmetals, ceramics, synthetics, etc., they may be utilized in a number of areas to obtain thermally stable joints.

An important feature of this invention as it relates to the preparation and use of adhesives is the solubility and stability of the prepolymers. These prepolymers can be stored and shipped without the extraordinary precautions heretofore required by polyimide adhesives. Using the prepolymers of this invention, various adherents, e.g., metal etc., may be coated with the polyimide prepolymers and then stored for substantial periods without employing elaborate precautions. The solubility and stability of the prepolymers allow subsequent polymerization bonding.

The coated adherents may be joined together employing moderate pressures at elevated temperatures. The preferred temperature range is from about 225 to about 375 C. plus or minus 20 C. The pressures applied to create an adherent bond at these temperatures range from less than atmospheric up to about 1000 p.s.i.

FORMATION OF LAMINATES AND COMPOSITES High strength laminates and reinforced fiber composites of improved thermal stability may be prepared from the prepolymer compositions described hereinbefore. The process of preparing these articles involves impregnating a reinforcing material which may be a fibrous material such as, for example, natural, synthetic, organic, inorganic, or metallic fibers etc., with an organic solution or dispersion containing an effective amount of a prepolymer of the type described above. Preferred fibrous materials include metal, glass, boron, and carbon. Alternatively, a solution of the amic acid prepolymer precursor or a mixture of the precursor and prepolymer may be used to impregnate the fibrous material. In either case, the solution used may contain from about 20 to 65% by Weight of solvent. Solvents suitable for use include all those hereinabove listed which may be employed in the making of prepolymers of their precursors.

Following impregnating or coating of the fibers with prepolymer solution, the impregnated materials are partially dried at temperatures from room temperature up to about 200 C. to remove a substantial amount of solvent. In this manner it is possible to obtain an intermediate having desirable tack and drape properties. The intermediate may then be cured by pyrolytic polymerization at temperatures of from about 225 C. to about 375 C. If desirable, pressures ranging up to 5,000 p.s.i. may be applied to aid in the formation of composite and laminate products.

PREPARATION OF COATINGS The polyamide-imide polymers of this invention may be used to form high-temperature resistant coatings which possess unusual stability and which are easy to process. Generally, conventional techniques may be employed to r 12 r form coatings of polymers according to this invention. Prepolymer is applied in neat or pigmented form to any of a wide variety of substrates including metals and nonmetals. Prepolymers of the composition disclosed herein, dissolved in highly polar solvents are placed on the substrate by conventional techniques such as spraying, spreading or dipping. Then, the final adherent coating is formed by pyrolytically polymerizing the prepolymer material. The conditions of polymerization are substantially as described above with respect to the formation of laminates and composites. 1

Objects may also be coated with the polymers of this invention by a fluid-bed technique. Using this method, a powdered polyamide-imide final polymer is formed by, for example, commuting a piece of the final cured polymer. Then, the powder is caused to form a fluid bed by suspension in fluid stream, preferably a gaseous stream. The object to be coated is then heated to a temperature at which the polymeric resin powder is thermosetting. The hot article is then brought into contact with the fluid bed where the powder makes contact, melts, flows to cover the object and then thermosets to yield the final coating.

PREPARATION OF MOLDING POWDERS In addition to the above-mentioned uses, prepolymers of the present invention may be used to form excellent molding powders, prepolymers are prepared in polar solvent and then desired particulate filler is added. The solvent is removed by evaporation at temperatures of from about 100 C. to about 200 C. Partial vacuums may also be employed as an aid in solvent removal. The resulting product is dried at nonpolymerizing temperatures to form a cake. This cake can be reduced to a powder by any of a number of conventional techniques such as, for example, milling, grinding or grating. The particulate particle size formed will depend upon the requirements of the subsequent molding process. Generally particle sizes ranging up to about 600 mesh are desired. Particles of this size range from about 1 to about 800 square meters per gram in surface area as measured by nitrogen absorption. The most preferred particle sizes are those having surface areas of from 50 to 600 square meters per gram.

Where the powder is to be employed in molds containing complex and intricate cavaties, it is often desirable to use a powder which has about 1% by Weight residual solvent content. Residual solvent content can be easily controlled by adjusting the time and temperature of the solvent removal and drying steps.

Molding powders prepared from prepolymers as described herein are suitable for a variety of purposes. They are particularly well suited for the preparation of moldlngs and coatings for high temperature applications. The final coating or molded product is formed by conventional techniques and at temperatures whereby the prepolymers are converted to final polymers by thermal polymerization.

If desirable, large amount of filler or reinforcing material, e.g., silica etc., may be added to the molding powders depending upon the ultimate intended use of the product. Various inorganic and organic fillers in the form of powders, or chopped fibers, may be used in combination with the polymeric compounds in amounts ranging up to about by Weight and more preferably in amounts of from about 10 to 60% by weight. These fillers include inorganic materials such as for example, silica, carbon, graphite, glass fibers, boron, metal oxides, clays, and various mixtures of these and any other known fillers.

DESCRIPTION OF THE BEST MODE FOR CARRYING OUT THE INVENTION The best mode of making prepolymers, precursors thereof, and final pyrolytically polymerized polyamideimide resins as presently contemplated is described hereinbelow with reference to the formation of specific prepolymers, precursors and polyamide-imide resins.

Example I Either of these compounds can be converted by thermal polymerization into a final polyamide-imide resin by heating at 275 C. for 30 minutes or more. The resulting product is a hard material capable of withstanding temperatures of up to about 250 C. without degradation for appreciable periods of time.

o Gila-ii-lI-Q-If-ii-CH; Example II H H Hexamethylene diamine and acetic anhydride are re- This compound is then reacted Wlth two H1016 eqlllvalents acted under conventional conditions to yield the followof trimellitic anhydride to form the following dianhydride i compound; compound:

To begin the preparation, p-phenylene diamine, an aromatic compound bearing two amino groups is reacted with acetic anhydride to form the following compound:

0 0 CHg--N-(CHzh-N-E-CE Ji 3 E 5 i i This compound is then reacted with two mole equivalents of trimellitic anhydride to form the following dill ll anhydride compound:

0 O Methylenedianiline is reacted with this compound and 3 E E g 3,6-endomethylene-1,2,3,6 tetrahydrophthalic anhydride, (nadic anhydride) all components being at equivalence. 0 1h 1!! 0 When these reactions take place at temperatures above about 200 C., the following prepolymer compound is 2 formed:

-CHz-N\QK] This compound may be recorded by applying heat or This dianhydride is then reacted with ethylene diamine vacuum to the solution to eifect solvent removal. and nadic anhydride; all reactants being at equivalence. When this reaction is carried out above about 200 C.,

the following prepolymer compound is formed:

At temperatures below about 200 C., the following corresponding amic acid precursor compound is formed:

This compound may also be recovered by solvent removal, to prevent imidization, the removal temperature This compound may be recorded by applying heat or must not exceed about 200 C. vacuum to effect solvent removal.

At temperatures below about 200 C., the following corresponding amic acid precursor compound is formed:

Example III 4,4'-methylenedianiline and acetic anhydride are reacted under conventional conditions to yield the following compound:

This compound is then reacted with two moles of trimellitic anhydride to form the following dianhydride compound:

This dianhydride is then reacted with ethylene diamine and nadic anhydride; all reactants being at equivalence. When this reaction is carried out above about 200 C., the following prepolymer compound is formed:

This compound may be recovered as in Example I.

dride is used rather than nadic anhydride. The result is "that the prepolymer 'or precursor of Example I is formed,

depending upon reaction temperature,but with the following end groupings:

o g p o H JL L CH N 0! CH:

C-OH

Generally the best mode of laminate formation involves impregnating a reinforcing material, e.g. glass cloth with either the amic acid precursor, or, the imidized prepolymer. Layers of impregnated cloth are stacked, pressed, and heated to imidize and/or cure the polymer.

More specifically, a high strength laminate is made by impregnating a glass fabric (Style 181, type E-A1100 soft finish) with a solution of the amic acid precursor as made in Example I above.

The glass coth is impregnated by immersion into a solution of the amic acid. Resin-content control is achieved by utilizing squeeze bars which provide a constant gap of about 0.018 inch. The impregnated fabric is dried at a temperature of about 150 F. Panels are prepared by At temperatures below about 200 C., the following laminating several plies of impregnated glass fabric. These corresponding amic-acid precursor compound is formed:

I II o This compound may be recovered as in Example I.

Either of these compounds can be converted by thermal polymerization into a final polyamide-imide resin by heating at 275 C. for about 30 minutes or more. The resulting product is a hard material capable of withstanding temperatures of up to about 250 C. for appreciable lengths of time without degradation in properties.

Example IV All of the reactions of Example I are carried out as in panels are subjected to imidization at about 400 F. for

about to 90 minutes and then cured at 600 F. under about 200 p.s.i. for '60 minutes to form a high strength laminate.

The best mode of composite structure formation involves impregnating a reinforcing fibrous material with a precursor compound prior to imidization and subsequently treating the impregnated material to first form a void-free prepolymer and then subjecting the composite to heatand pressure to form a structure consisting of a reinforcing material embedded within a final cure p ythat example with the exception that methyl nadic anhyamide-imide.

More specifically, boron filament prepregs are prepared utilizing Mylar film (terephthalic acid polyester) which is tightly fitted to the circumference of a drum and secured at the overlap with tape.

A solution containing approximately 40% of an amic acid precusor as prepared in Example I above, in dimethyl formamide is applied to the Mylar surface followed by a piece of scrim cloth which is placed onto the film. While the drum is slowly rotated, the impregnated scrim cloth is dried by using an industrial hot-air gun until the resin is sufliciently dry to avoid any sagging. An additional coat of the polyamide-acid solution is applied to the impreg nated scrim cloth surface and predried in the same manner. The boron filaments are fed to one end of the drum and secured with a small piece of tape. The prewound boron filaments are then coated by applying the polyamideacid solution and again dried in the same manner indicated hereinabove. The prepregs is subsequently removed from the drum and dried in an oven at a temperature of about 85 C. for about 30 minutes and the Mylar film is then removed. The prepreg is cut into rectangular pieces and staged in two steps by (1) placing them in an air-circulating oven at 177 C. for about five minutes, (2) cooling them between fiat metal plates and then repeating this process at an oven temperature of about 246 C. The thickness of the finished prepreg is approximately 0.006 to 0.007 of an inch. The finished prepreg is stable in air and has no particular storage or handling problems. Laminates may be prepared from 10 layers of the polyamideacid, boron prepregs by molding the prepregs in a press at about 315 C. After inserting the stacked plies into the heated press, they are subjected to a contact pressure for 90 seconds and then the full molding pressure of 100 p.s.i. for about 60 minutes cycle.

As alternative to the above process, it is possible to utilize the steps described up to the point of removing the tape from the drum. At this point, the tape is dried partially, e.g., up to about 90% by Weight of the solvent may be removed to obtain an intermediate prepreg characterized as having tack and drape. These intermediates may have up to about 10% by weight of the solvent remaining the prepreg. However, it is obvious that all of the solvent may be removed, e.g., to 100%, from the prepreg prior to removing the tape from the drum. It should be noted that the tacky prepregs normally have an advantage over the completely or substantially dried prepregs in preparing contour parts because it facilitates the layup of unusual shapes by minimizing ply slippage. In order to prepare void-free articles by this process, it is necessary in the fabrication step toimidize the amic acid precursor, in situ, after layup in stacked plies at about 246 C. at atmospheric pressure prior to raising the tempertaures to 315 C. and applying 100 p.s.i. mechanical pressure. This imidization at low temperature is desirable to permit the escape of the volatile condensation products prior to initiating resin flow.

As another alternative, the control of the resin content may be maintained by preparing a prepreg of thinlightweight glass scrim cloth having as much as 90% resin. The resin is applied to the scrim cloth in the form of an amic acid precursor in an organic solvent. The high resin content prepreg is subsequently laid onto the winding drum and the boron filament is wound into the prepreg. The resultant boron-impregnated prepreg is removed from the drum, imidized and molded in a manner similar to that described above. As a further alternative, it is obvious that it is possible to perform as an alternative to wind the boron filaments onto the drum first without the addition of the polyamide-acid solution and then subsequently applying the polyamide-acid prepreg on top of the prewound boron.

The best mode of adhesive formation and use involves coating the surface of selected adherents with a melt, slurry or varnish of a prepolymer, precursors of the pre- 18 polymers or mixtures thereof, and joining the adherents together with heat and pressure.

More specifically, a strong adhesive bond is made by coating a surface of two different types of metal articles with an amic acid solution of the type described above in connection with the best mode of composite formation. The surfaces are brought together and preheated at about 150 C. in a forced air oven for about one hour. Subsequently, the temperature is increased to about 250 C. for an additional hour to complete imidization of the polymer. The bond is then heated at 350 C. and subjected to a pressure of about 200 p.s.i. until a strong bond is formed between the surfaces.

The best mode of preparing coatings according to this invention is substantially the same as laminate, composite, or adhesive formation with the exception that the precursor or prepolymer is cured without pressure and while in contact with a substrate only.

The best mode of preparing molding powders according to this invention involves forming a final cured resin as described hereinabove, and grinding the solid resin to the desired size.

More specifically, a final polymer solid, resin product is prepared by curing at 275 C. for 30 minutes the prepolymer made in Example I above. The resulting solid product is ground on a ball mill to form a powder of about 60 mesh. This powder may be mixed with an equal amount of a 300 mesh silica flour and pressed for about 55 minutes at 325 p.s.i. and at a temperature of about 315 C. to form a molded product having a smooth,

uniform surface and a Barcol hardness of about 65.

Several important advantages may be obtained by using the present invention in the manner heretofore described. High performance with regard to temperature stability and resistance to oxidation is inherent with the use of these materials. However, this high performance is obtainable at a lower cost than had been believed possible before these present discoveries. In addition, the polymers of this invention possess superior flow and adhesive properties allowing for the preparation of superior laminates, composites, coatings, adhesives and molding compositions.

Whereas the invention has now been particularly described with reference to the preferred embodiments thereof and with further reference to the best presently contemplated mode of making and using, it will be readily apparent to those of ordinary skill in the art that various other adaptations and modifications of the invention are possible without departing from the spirit and scope of the invention as set forth in the appended claims.

For example, whereas the prepolymers, precursors and final polymers have been described in the examples as specific compounds, it will be readily apparent to those skilled in the art of that the family of compounds as described hereinabove by Way of generic formula may be made and used according to the teachings of this invention. Thus, Y through Y Y Y R R R and n may vary within all the limits cited without departing from the invention as their choice is not critical so long as the teachings of the invention are followed.

I claim:

1. A mixture of polymers characterized by the aggregate formula it E t it R and R are, for each constituent polymer, individually R is for each constituent polymer, selected from the for the aggregate mixture, is statistically greater than 0.

selected from the class consisting of where: X is a member of the class consisting of carbon, oxygen, sulfur, and carbonyl, Y through Y Y and Y when present, are individually selected from the class consisting of hydrogen, aromatic groups, substituted aromatic groups, saturated or unsaturated hydrocarbon groups having from 1 to 6 carbon atoms, alkyl ethers, aryl ethers, halogens, and nitro groups;

selected from the class consisting of aromatic groups,

substituted aromatic groups, saturated and unsaturated hydrocarbon groups, saturated and unsaturated heterocyclic groups, and mixtures thereof;

class consisting of substituted aromatic groups, unsubstituted aromatic groups, saturated cyclic groups, unsaturated cyclic groups, saturated heterocyclic groups,

and unsaturated heterocyclic groups; and

2. The mixture of claim 1 wherein R is an aromatic group.

3. The mixture of claim 2 wherein R is a phenylene group.

4. The mixture of claim 1 wherein 1 represents an amount suflicient to form compounds having a molecular weight ranging from about 500 to about 6,000.

5. The mixture of claim 1 wherein R R and R are aromatic groups.

6. The mixture of claim 1 wherein 17 is from about 1 to about 10.

7. A mixture of polymers characterized by the aggregate formula and where: X is a member of the class consisting of carbon, oxygen, sulfur, and carbonyl, Y through Y and Y and Y when present, are individually selected from the class consisting of hydrogen, aromatic groups, su-bstituted aromatic groups, satured or unsaturated hydrocarbon groups having from 1 to 6 carbon atoms, alkyl ethers, aryl ethers, halogens, and nitro groups;

R and R are, for each constituent polymer, individually selected from the class consisting of aromatic groups, substituted aromatic groups, saturated and unsaturated hydrocanbon groups, saturated and unsaturated heterocyclic groups, and mixtures thereof;

R is, for each constituent polymer, selected from the class consisting of substituted aromatic groups, unsubstituted aromatic groups, saturated cyclic groups, unsaturated cyclic groups, saturated heterocyclic groups and unsaturated heterocyclic groups; and

1 for the aggregate mixture, is statistically greater than 0. 8. The mixture of claim 7 wherein R is an aromatic group. a

9. The mixture of claim 8 wherein R is a phenylene group.

10. The mixture of claim 7 wherein n represents an amount sufiicient to form compounds having a molecular weight ranging from about 500 to about 6,000.

11. The mixture of claim 1 wherein R R and R are aromatic groups.

12. The mixture of claim 7 wherein n is from about 1 to about 10.

13. A polymeric mixture comprising a first portion consisting of compounds represented by the formula:

l t i E If].

E and E are, for each constituent compound, individually selected from the class consisting of and 21 E and E, are, for each consituent compound, individually selected fr om the cl ass consisting t p and Y] E H H: l, COH Ya where:

X is a member of, the class consisting of carbon, oxygen, sulfur, and carbonyl, Y through Y and Y and Y when present, are individually selected from the class consisting of hydrogen, aromatic groups, substituted aromatic groups, saturated or unsaturated hydrocarbon groups having from 1 to 6 carbon atoms, alkyl ethers, halogens, and nitro groups;

R and R are, for each constituent compound, individually selected from the class consisting of aromatic groups, substituted aromatic groups, saturated and unsaturated hydrocarbon groups, saturated and unsaturated heterocyclic groups, and mixtures thereof;

R is, for each constituent compound, selected from the class consisting of substituted aromatic groups, unsubstituted aromatic groups, saturated cyclic groups, unsaturated cyclic groups, saturated heterocyclic groups and unsaturated heterocyclic groups; and

1; is statistically greater than 0.

and

and mixtures thereof:

where:

X is a member of the class consisting of carbon, oxygen, sulfur, and carbonyl, Y through Y and Y and Y when present, are individually selected from the class consisting of hydrogen, aromatic groups, substituted aromatic groups, saturated and unsaturated hydrocarbon groups having from 1 to 6 carbon atoms, alkyl ethers, aryl ethers, halogens, and nitro groups.

16. The process of claim 15 wherein said imide is formed by the reaction of a primary polyfunctional amine and an anhydride represented by the formula:

where R is a lower alkyl radical having from 1 to 5 carbon atoms.

17. The process of claim 15 wherein said second anhydride is added as the last reactant.

18. A process for preparing the polymers of claim 7 comprising the steps of reacting an amide with a first anhydride to form a dianhydride, and reacting at temperatures below about 200 C., said dianhydride with a primary polyfunctional amine and a second anhydride selected from the group consisting of X is a member of the class consisting of carbon, oxygen, sulfur, and carbonyl, Y through Y Y and Y when present, are individually selected from the class consisting of hydrogen, aromatic groups, substituted aromatic groups, saturated or unsaturated hydrocarbon groups having from 1 to 6 carbon atoms, alkyl ethers, aryl ethers, halogens, and nitro groups. 19. The process of claim 18 wherein said imide is formed by the reaction of a primary polyfunctional amine and an anhydride represented by the formula:

0 Rik where R is a lower alkyl radical having from 1 to 5 carbon atoms.

20. The process of claim 18 wherein said second anhydride is added as the last reactant.

21. Polymers formed by pyrolytically polymerizing at a temperature of from about 225 C. to about 375 C. compounds represented by at least one member of the group of formulae consisting of ll 0 o where: where: .7 E and E are individually selected from the class con- E and B are individually selected from the class consistsisting of m y Yzo and and lc/ C/' Y A a I g o e E3 and B4 are individually Selected f h class where: X is a member of the class conslstmg of carbon, sisting of oxygen, sulfur, and carbonyl Y through Y Y and Y0 Y when present, are individually selected from the class consisting of hydrogen, aromatic groups, sub- 0 H stituted aromatic groups, saturated or unsaturated hyg l drocarbon groups having from 1 to 6 carbon atoms,

alkyl ethers, aryl ethers, halogens, and nitro groups; 0 R and R are individually selected from the class cong sisting of aromatic groups, substituted aromatic groups, Y1 saturated and unsaturated hydrocarbon groups, saturated and unsaturated heterocyclic groups, and mixtures thereof; and R is selected from the class consisting of substituted aro- 0 H matic groups, unsubstituted aromatic groups, saturated 1 cyclic groups, unsaturated cyclic groups, saturated heterocyclic groups and unsaturated heterocyclic groups; Y c-orr and l 1; is one or more.

27. The polymers of claim 26 wherein '1 is an integer where: X is a member of the class consisting of car- 40 of fmm 1 bon, oxygen, sulfur, and carbonyl, Y through Y and The P y of claim 26 wherein 3 is a p Y and Y when present, are individually selected from 8116 P- the class consisting of hydrogen, aromatic groups, sub- Polymers chafacterlled y the formula:

stituted aromatic groups, saturated or unsaturated hy- A O o drocarbon groups having from 1 to 6 carbon atoms, H I5 0 0 a H alkyl ethers, aryl ethers, halogens, and nitro groups; H g \I sisting of aromatic groups, substituted aromatic groups,

R and R are individually selected from the class cona s\ NR1E| H0O H H 0-011 saturated and unsaturated hydrocarbon groups, saturated and unsaturated heterocyclic groups, and mixtures thereof; where: R is selected from the class consisting of substituted aro- E and B are individually selected from the class conmatic groups, unsubstituted aromatic groups, saturated sisting of: cyclic groups, unsaturated cyclic groups, saturated Y6 heterocyclic groups and unsaturated heterocyclic groups; E f; and g 0 H 1; is statistically greater than 0. Y t I 1 22. The polymers of claim 21 wherein the predominate YPXJYB portion consists of the first member of said group of Y4 formulae. A

23. The polymers of claim 21 wherein the predominate portion consists of the second member of said group of formulae. and

24. Polymers of claim 21 wherein n is from about 1 to about 10. v Y Y, 0 i 25. Polymers of claim 21 having a molecular weight i k-N- in excess of 10,000. v

26. Polymers characterized by the general formula: 9-011 A }L I 0 where: X is a member of the class consisting of carbon, oxygen, sulfur, and carbonyl, Y through Y and Y and Y when present, are individually selected from I- G C J the class consisting of hydrogen, aromatic groups, substituted aromatic groups, saturated or unsaturated hy- 25 drocarbon groups having from 1 to 6 carbon atoms, 31. The polymers of claim 30 wherein R is a phenylalkyl ethers, aryl ethers, halogens, and nitro groups; e e gr p. R and R are individually selected from the class con- References Cited sisting of aromatic groups, substituted aromatic groups, UNITED STATES PATENTS saturated and unsaturated hydrocarbon groups, satu- 5 3 355 427 11/1967 Loncrini 260 47 rated and unsaturated heterocyclic groups, and mix- 3:179:634 4/1965 Edwards 260 78 Wes thereof; 3,485,796 12/1969 Naselow 26047 R is selected from the class consisting of substituted 3,435,002 4 19 9 l b 25 4 5 aromatic groups, unsubstituted aromatic groups, satu- 3,565,549 2/1971 Lubowitz 117--126 rated cyclic groups, unsaturated cyclic groups, saturated heterocyclic groups and unsaturated heterocyclic ALLAN LIEBERMAN Primary Exammer groups; and R. ZAITLEN, Assistant Examiner tt't'll tth 0. 1 is s a 1s rca y grea er an Us. cl. XR.

30. The polymers of claim 29 wherein 1 is an integer 15 of from about 1 to 10, 260-302, 30.4 N, 32.6 NT, 857 P1 

